The present invention relates to mobile telecommunications systems and, in particular, to declaring correctness of frame reception.
Basic second generation mobile telecommunications systems such as IS-95 use a cyclic redundancy code (CRC) checksum for out-of-synchronization detection in a mobile terminal of a mobile telecommunications network. If the checksum calculated from the received transmission is not the same as transmitted, then an error is declared, and the uplink can be shut off, for instance. In third generation systems, CRC has been mentioned for use for the same purpose. For instance, the out-of-synchronization condition for WCDMA (wideband code division multiple access) needs to be determined by the terminal. However, using only CRC is not possible for WCDMA, as in IS-95, since there are services without CRC and also services such as AMR (adaptive multi-rate) speech transmit during DTX (discontinuous transmission) frames without CRC information being present. In second generation, the services are mainly speech services, and CRC is used. In third generation, the variety of services is very broad, and there are cases where CRC is not needed.
The object of the present invention is to use other information to aid not only in the out-of-synchronization detection, but also, in general, for determining or declaring correct or incorrect frame reception by a terminal of a mobile telecommunications network.
According to the invention, received transport channels for a correct checksum or for a transport format combination indicator (TFCI) are checked and correctness of reception of said channels declared according to said CRC check or said TFCI check. Various methods and apparatus for carrying out the invention are shown below in detail.
Thus, the invention can be for use in a terminal of a mobile telephone system having a plurality of base stations capable of communication with the terminal over corresponding radio up and down links, wherein it is determined in the terminal whether in a downlink from a base station to the terminal a cyclic redundancy code checksum is present and correct and if so, correct reception of the downlink is declared and, if not present, it is determined in the terminal from any transport format combination indicator signal present in the downlink from the base station to the terminal whether a discontinuous transmission (DTX) frame is present or not and if not, incorrect reception of the downlink is declared, but, if so, correct reception of the downlink is declared. It is also possible to utilize transmission quality information obtained from the DTX frame for providing an outer loop power control quality target setting signal. The power control quality target setting signal can be provided to the base station in an uplink from the terminal to the base station. The declaration of incorrect/correct reception is for an out-of-synchronization condition or an in-synchronization condition of the downlink.
Another way to carry out the invention is to determine in the terminal whether a downlink from a base station to the terminal contains a zero rate transport format combination indicator (TFCI) for transmission time intervals (TTIs) in a frame and if so, the frame is declared to be in-synchronization, and if not, cyclic redundancy checksums (CRCs) are checked for the TTIs and if at least one is correct, the frame is declared to be in-synchronization. Further, if at least one CRC is not correct, it can be determined in the terminal if dedicated physical control channel (DPCCH) quality and CRC history is over a threshold for an averaging window and if so, the frame can be declared to be in-synchronization and otherwise the frame declared to be out-of-synchronization.
Still another way to carry out the invention is, if a zero rate transport format combination indicator (TFCI) is determined to be present in a transport channel, correct transport block reception is declared, and a block error rate count incremented and, if not, cyclic redundancy codes (CRCs) of transport blocks in a transmission time interval (TTI) are checked, and in the presence of correct CRCs, the block error rate count is incremented.
The present invention advantageously offers criteria for determining correct or incorrect frame reception for all service combinations of a third generation mobile telecommunications system. It is independent of the received signal power level. This method can be used, for instance, for declaring an out-of-synchronization condition, as a block error rate (BLER) indication during DTX frames for outer loop operation, or the like.